The formula of the volume of a rectangular prism is
[tex]V=l\cdot w\cdot h[/tex]where l is the length, w is the width and h is the height
In our case we have
l=6ft
w=6ft
h=15ft
we substitute the values
[tex]V=6\cdot6\cdot15[/tex]the volume is
[tex]V=540ft^3[/tex]the volume is 540 cubic feet